Microwave oven in which rush current to high voltage transformer is suppressed

Abstract

When power supply to a high voltage transformer starts, the phase θ of the voltage of an AC power source when power supply to the high voltage transformer is stopped last time is referred to. In accordance with the value of the phase θ, the phase of the voltage of the AC power source when power supply to the high voltage transformer starts is determined, so that the peak value of the rush current in the high voltage transformer is minimized.

What is claimed is:  
     
       1. A microwave oven, comprising: 
       a magnetron heating food;  
       a high voltage transformer supplying a high voltage to said magnetron; and  
       a control unit enabling switching between presence/absence of power supply from a prescribed AC power source to said high voltage transformer, and capable of detecting power supply voltage phase as a phase of the voltage supplied by said prescribed AC power source; wherein  
       said control unit starts power supply to said high voltage transformer with a power supply voltage phase in accordance with said power supply voltage phase at a time point when power supply to said high voltage transformer is stopped last time.  
     
     
       2. The microwave oven according to  claim 1 , wherein 
       said control circuit starts power supply to said high voltage transformer at a time point when said power supply voltage phase is at a specific phase, if said power supply voltage phase at a time point when power supply to said high voltage transformer is stopped last time cannot be detected.  
     
     
       3. A microwave oven according to  claim 1 , further comprising: 
       a heating chamber accommodating food;  
       a display unit capable of displaying a state of said microwave oven; and  
       a temperature detecting unit detecting a temperature in said heating chamber; wherein  
       manner of display on said display unit changes in accordance with a temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       4. The microwave oven according to  claim 3 , wherein 
       said display unit is capable of displaying symbols, and display color of the symbols on said display unit changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       5. The microwave oven according to  claim 3 , wherein 
       said display unit is implemented by a liquid crystal display device with a back light, and  
       display color of said back light changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       6. The microwave oven according to  claim 3 , wherein 
       said display unit terminates displaying operation, provided that the temperature detected by said temperature detecting unit attains to a prescribed temperature or lower, after termination of heating by said magnetron.  
     
     
       7. The microwave oven according to  claim 3 , wherein 
       said control unit is supplied with power from a prescribed power source, and power supply to the control unit is terminated provided that the temperature detected by said temperature detecting unit attains to a prescribed temperature or lower.  
     
     
       8. A microwave oven, comprising: 
       a magnetron heating food;  
       a high voltage transformer supplying a high voltage to said magnetron; and  
       a control unit enabling switching between presence/absence of power supply from a prescribed AC power source to said high voltage transformer, and capable of detecting a power supply voltage phase as a phase of the voltage supplied by said prescribed AC power source; wherein  
       said control unit stops power supply to said high voltage transformer at a time point when said power supply voltage phase attains to a prescribed phase, if a condition to terminate heating by said magnetron is satisfied.  
     
     
       9. The microwave oven according to  claim 8 , wherein 
       said control circuit starts power supply to said high voltage transformer at a time point when said power supply voltage phase is at a specific phase, if said power supply voltage phase at a time point when power supply to said high voltage transformer is stopped last time cannot be detected.  
     
     
       10. A microwave oven according to  claim 8 , further comprising: 
       a heating chamber accommodating food;  
       a display unit capable of displaying a state of said microwave oven; and  
       a temperature detecting unit detecting a temperature in said heating chamber; wherein  
       manner of display on said display unit changes in accordance with a temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       11. The microwave oven according to  claim 10 , wherein 
       said display unit is capable of displaying symbols, and  
       display color of the symbols on said display unit changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       12. The microwave oven according to  claim 10 , wherein 
       said display unit is implemented by a liquid crystal display device with a back light, and  
       display color of said back light changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       13. The microwave oven according to  claim 10 , wherein 
       said display unit terminates displaying operation, provided that the temperature detected by said temperature detecting unit attains to a prescribed temperature or lower, after termination of heating by said magnetron.  
     
     
       14. A microwave oven, comprising: 
       a magnetron heating food;  
       a high voltage transformer supplying a high voltage to said magnetron;  
       a relay capable of assuming a first state in which a prescribed AC power source is electrically connected to said high voltage transformer, and a second state in which connection between said prescribed AC power source and said high voltage transformer is canceled; and  
       a control unit controlling an operation of said relay; wherein  
       said control unit controls said relay to perform under a preliminary operating condition from said second state working toward said first state but not reaching said first state, followed by switching from the preliminary operating condition to said first state.  
     
     
       15. The microwave oven according to  claim 14 , wherein said control unit makes said relay perform said preliminary operating condition a plurality of times. 
     
     
       16. The microwave oven according to  claim 14 , wherein said control unit returns said relay to said second state, after said relay performs said preliminary operating condition. 
     
     
       17. A microwave oven according to  claim 14 , further comprising: 
       a heating chamber accommodating food;  
       a display unit capable of displaying a state of said microwave oven; and  
       a temperature detecting unit detecting a temperature in said heating chamber; wherein  
       manner of display on said display unit changes in accordance with a temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       18. The microwave oven according to  claim 17 , wherein 
       said display unit is capable of displaying symbols, and  
       display color of the symbols on said display unit changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       19. The microwave oven according to  claim 17 , wherein 
       said display unit is implemented by a liquid crystal display device with a back light, and  
       display color of said back light changes in accordance with the temperature detected by said temperature detecting unit, after termination of heating by said magnetron.  
     
     
       20. The microwave oven according to  claim 17 , wherein 
       said display unit terminates displaying operation, provided that the temperature detected by said temperature detecting unit attains to a prescribed temperature or lower, after termination of heating by said magnetron.